Coaxials - Reality vs. Experience?

what is the definition of "acoustic center" ?

@herbreichert The point in space from which sound appears to originate in terms of time.  Think of a woofer and tweeter mounted on a flat baffle.  Look at it from the side.  The tweeter's acoustic center is practically at the baffle, but the woofer's may be 1" or more behind the baffle.  Speaker designers have to take this into consideration for either phase or time alignment.

how do we know when they are aligned? A tone burst?

Kind of depends how you mean "alignment." Phase aligned you can tell by an smooth transition from one driver to the other. Time aligned you can see using a step response. See figure 9 in these measurements for time aligned speaker step response.

what is the definition of a point source?

A theoretical "ideal" (one of many ideals) in which the full range of sound appears to come from a single point in space. A single, full-range driver is by definition a point source. Some multi-way speakers may attempt to mimic this behavior in time and space. The Duntech Sovereign is a famous, early-ish example.

Contrast to a line-source, like the famous Infinity RS.

@herbreichert PS - Your typical 2 or 3 way speaker is neither a point nor a line source. Vandersteen may be time and phase aligned but it’s not a point source.

That perfect step response in the Stereophile measurements goes out the window when you stand up. :)

A true point source maintains it's time alignment no matter where you measure it from.

I managed to wrestle the keyboard from my wife😅. @herbreichert C'mon, Herb none of this false modesty! You know we know you're a pretty sharp guy! I Know old wisdom says not to let on how smart one really is 😉.

Can we get some initial impressions of the Heretic? We can keep a secret until the review. 

You must be totally confused by one of the bullet points on their site:

                   POINT SOURCE CO-AXIAL TRANSDUCERS

"All sounds originate from a single point in space. No transducers all over the place, yielding fuzzy, phasy music reproduction. Excellent soundstage, precise location of instruments and coherency."

Love this hobby.

Truly appreciate you, Herb!

OOPS. After reading the previous few posts. I should make a correction. I know you are a pretty sharp guy!

I’m an Ohm and KEF fan these days. I heard the new Mobile Fidelity Sourcepoints and those caught my ear. In a larger room from further away the inherent coherency of this kind of design matters less.